The present invention relates to an ultrasonic imaging method and apparatus employing a microballoon contrast agent.
In ultrasonic imaging employing a contrast agent, the contrast agent comprises a large number of bubbles (microballoons) having a diameter on the order of a few micrometers in a liquid, and secondary harmonics echoes based on the non-linear echo source property of the microballoons is utilized to achieve the contrast imaging. The nonlinear echo source property arises from resonance of the microballoons with the frequency of the transmitted ultrasound.
Since the microballoons continue to resonate after the ultrasound pulse transmission is terminated, echo signals generated by the microballoons include, in addition to the main echo corresponding to the pulse width of the transmitted ultrasound, subsequent tailing. Each echo signal has a main echo return time representing the depth of the reflecting point, and hence the signal tailing causes image tailing in the image of the reflecting point. Accordingly, the generated contrast image has poor sharpness.